The present invention relates to method and apparatus for providing alignment of elements such as optical fibers in a predetermined array.
Fiberoptics is used in the communication industry for high levels of data transport. As a result, optical fibers need to be coupled in with precision to semiconductors, detectors, and mirrors in arrays.
A method for obtaining precision accuracies is to use photolithography to image a mask of array openings on a substrate such as silicon. Silicon is chosen because it has a low thermal coefficient equal to that of silicon substrates that optical fibers match into. Using a photolithographic mask, the openings of the array are etched in the silicon wafers. The problem with this method is that to produce an accurately sized opening, plasma etching must be performed anisotropically which produces a near vertical opening. For small openings such as those for 125 micrometer diameter single mode optical fibers which are nominally 124-126 micrometers in diameter, the depth of the etched opening in the silicon substrate is nominally 500-700 micrometers. This etching can be performed with Reactive Ion Etching which is a very slow process that produces a steep narrow opening at both ends of the substrate. The slow etch rate makes it costly to fabricate, and the small opening size makes it difficult to insert the optical fiber into the opening during array fabrication.
If a silicon substrate is etched faster with standard plasma etching or with wet chemical etching, the etching is isotropic. The problem with such faster etching technique is that there is less control over the size of the openings at both ends of the substrate because of non-uniform etch rates across the face of the substrate. As a result, the openings can have large variations in diameter and, consequently, cause inaccuracies in the placement of optical fibers in the plane of the substrate.
A prior art optical fiber array connector uses a substrate having rear and forward surfaces and a plurality of openings that communicate through these surfaces. Each opening in the mask element or substrate is laser drilled and has a diameter which is smaller than the outer diameter of a cladding of an optical fiber to be inserted therethrough. Each opening is either cylindrical in shape or flared outwards from the rear to the forward surface. Each of the plurality of optical fibers has an end having truncated side surfaces forming a cone that extends through a separate opening of the substrate so that the conical surface of the optical fiber engages the circumference of the separate opening adjacent the rear surface of the substrate where the two diameters are equal. After the plurality of optical fibers are inserted into their respective openings in the substrate, the optical fibers are bonded to the substrate by applying a bonding (adhesive) material over the forward surface of the substrate which also fills the remaining openings between the conical surfaces of the optical fibers and the substrate. The exposed conical tips of the optical fibers and the bonding material are then ground and polished to truncate the cones and expose the optical fiber core diameters.
One problem presented with this type of prior art optical fiber array connector is that the taper etching of the optical fiber has to be uniform to assure self-centering. The insertion of just the conical tip of the optical fiber can present other problems with annular alignment as well as bonding (attaching) of the optical fiber to the substrate. There can also be a large variation in the size of each opening during etching or laser drilling. This means that some of the openings could be larger than the diameter of the optical fiber. This can cause inaccuracies in the placement of the optical fiber. If an opening is too small, it can present problems in firmly securing the tips of the optical fibers with epoxy or other bonding material.
It is desirable to provide an array of elements, such as optical fibers, in which alignment (i.e., center-to-center spacings of the elements ) of xc2x12.0 micrometers is repeatedly achievable using current photolithography and electroforming technology.
The present invention is directed to method and apparatus for providing alignment of an array of elements such as optical fibers to a preselected center-to-center tolerance value.
From a first apparatus aspect, the present invention is an optical fiber array apparatus. The optical fiber apparatus comprises a relatively thick primary substrate and a relatively thin first layer. The relatively thick primary substrate has sufficient structure to support an array of N spaced-apart optical fibers, has first and second opposing surfaces, and defines a plurality of N primary substrate apertures which each extend therethrough from the first surface to the second surface. A cross-section of each of the N substrate apertures is greater than a cross-section of an optical fiber such that one optical fiber can be passed through in each of the N primary substrate apertures. Each optical fiber comprises a cladding layer surrounding an optical core. The relatively thin first layer, which has insufficient structure by itself to support an array of N spaced-apart optical fibers, engages the second surface of the primary substrate and defines N apertures therethrough with centers of the first layer apertures being aligned to a preselected tolerance value which is that required for the array of optical fibers. The size of the cross-section of each of the first layer apertures is less than the size of the cross-section of each primary substrate aperture. Each first layer aperture is within a footprint of one of the primary substrate apertures such that optical fibers inserted through the primary substrate apertures enter the first layer apertures. The cross-sections of the first layer apertures having limited variations that result in spacings between adjacent optical fibers placed in the primary substrate apertures and entering the first layer apertures being within the preselected tolerance value such that optical fibers are aligned within the preselected tolerance value.
From a second apparatus aspect, the present invention is an optical fiber array apparatus. The optical fiber apparatus comprises a relatively thick primary substrate and a relatively thin layer. The relatively thick primary substrate has sufficient structure to support an array of N spaced-apart optical fibers, has first and second opposing surfaces, and defines a plurality of N primary substrate apertures which each extend therethrough from the first surface to the second surface with a cross-section of each of the N substrate apertures being greater than a cross-section of an optical fiber such that one optical fiber can be passed through in each of the N primary substrate apertures. Each optical fiber comprises a cladding layer surrounding an optical core. The relatively thin first layer, which has insufficient structure by itself to support an array of N spaced-apart optical fibers, engages the second surface of the primary substrate and defines N apertures therethrough with centers of the first layer apertures being aligned to a preselected tolerance value which is that required for the array of optical fibers. The size of a portion of a cross-section of each of the first layer apertures is less than the size of the cross-section of each primary substrate aperture and is greater than the cross-section of a cladding layer and an optical core. Each first layer aperture is within a footprint of one of the primary substrate apertures such that the cladding layers and the surrounded optical cores inserted through the primary substrate apertures pass can pass through the first layer apertures. The cross-sections of the first layer apertures have limited variations that result in spacings between the cladding layers of adjacent optical fibers passing through the primary substrate apertures and the first layer apertures being within the preselected tolerance value such that the optical fibers are aligned within the preselected tolerance value.
From a first method aspect, the present invention is a method of forming an array apparatus, which supports N spaced-apart optical fibers to a preselected tolerance value. The method comprises the steps of: (a) forming, in a relatively thick primary substrate having sufficient structure to support an array of N spaced-apart optical fibers, N substrate apertures which each extend therethrough from a first surface of the primary substrate to a second surface of the primary substrate with a cross-section of each of the N primary substrate apertures being greater than a cross-section of an optical fiber such that one optical fiber can be passed through each of the N primary substrate apertures; (b) forming a relatively thin first layer defining N apertures therethrough with centers of the layer apertures being aligned to the preselected tolerance value which is that required for the array of optical fibers, the size of the cross-section of each of the layer apertures being less than the size of the cross-section of each primary substrate aperture; (c) locating the relatively thin first layer on the second surface of the primary substrate with each first layer aperture being within a footprint of one of the primary substrate apertures such that optical fibers inserted through the primary substrate apertures make contact with the first layer apertures, and the cross-sections of the first layer apertures having limited variations that result in spacings between adjacent optical fibers placed in the primary substrate apertures and in contact with the first layer apertures such that the optical fibers are aligned within the preselected tolerance value; (d) inserting each of the N optical fibers through a separate aperture in the primary substrate and through a separate aperture in the first layer which is within the footprint of the primary substrate aperture; and (e) applying a bonding material to the plurality of N optical fibers in their associated apertures in the primary substrate so as to attach the N optical fibers to the primary substrate with the optical fibers being aligned to the preselected tolerance value.
From a second method aspect, the present invention is a method of forming an optical fiber array apparatus, which comprises an array of N spaced-apart optical fibers aligned to a preselected tolerance value. The method comprises the steps of: (a) forming, in a relatively thick primary substrate having sufficient structure to support an array of N spaced-apart optical fibers, N substrate apertures which each extend therethrough from a first surface of the primary substrate to a second surface of the primary substrate with a cross-section of each of the N primary substrate apertures being greater than a cross-section of a cladding layer and optical layer of an optical fiber such that the cladding layer of an optical fiber can be passed through each of the N primary substrate apertures; (b) electroforming a relatively thin metal first layer defining N apertures therethrough with centers of the first layer apertures being aligned to the preselected tolerance value which is that required for the array of N spaced-apart optical fibers, the size of the cross-section of each of the first layer apertures being less than the size of the cross-section of each primary substrate aperture; (c) locating the relatively thin metal first layer on the second surface of the primary substrate with each first layer aperture being within a footprint of one of the primary substrate apertures such that optical fibers inserted through the primary substrate apertures make contact with the first layer apertures, and the cross-sections of the first layer apertures having limited variations that result in spacings between adjacent optical fibers placed in the primary substrate apertures and in contact with the first layer apertures such that the optical fibers are aligned within the preselected tolerance value; (d) inserting each of the N optical fibers through a separate aperture in the primary substrate and through a separate aperture in the first layer which is within the footprint of the primary substrate aperture; and (e) applying a bonding material to the plurality of N optical fibers in their associated apertures in the primary substrate so as to attach the N optical fibers to the primary substrate with the optical fibers being aligned to the preselected tolerance value.
The invention will be better understood from the following more detailed description taken with the accompanying drawings and claims.